In general, when two metals are connected to each other and are immersed in sea water, or other salt solutions that are not too acid or alkaline, there will be a corrosive action only if the metals are dissimilar. If the metals are dissimilar, electrochemical corrosion will occur and one metal will be anodic to (i.e. corroded by) the other metal, which will be rendered cathodic. This problem of electrochemical corrosion is prevalent in seawater piping systems in which leaking may occur at pipe joints.
In an effort to overcome the problem of corrosion, a number of different anticorrosion systems or electrical insulation systems have been proposed. For example, Gush (U.S. Pat. No. 1,514,903) describes an anticorrosion device suitable for water-cooling apparatus of internal combustion engines. A thin insulating sleeve is used to separate an electrode from the wall of the structure. Boyd (U.S. Pat. No. 1,592,172) and Bradford (U.S. Pat. No. 4,345,785) utilize an electrical insulating gasket between sections of metal pipes. Burger et al (U.S. Pat. No. 4,406,467) and Kohn (U.S. Pat. No. 4,776,600) utilize reinforced dielectric pipe flange gaskets. Weigl (U.S. Pat. No. 4,848,804) describes a dielectric tube coupling in which insulation is provided by sleeves surrounding the outside of the tube.
A drawback to each of these prior art apparatus is the close proximity of dissimilar metals. Even though direct contact is prevented by the insulation material, the separation boundary is too small to adequately prevent galvanic action.